The present invention relates to the installation of seal rings in valve housings and in particular to the installation of seal rings in the housing of disc valves.
Expired U.S. Pat. No. 3,442,488 discloses a disc valve in which a disc is pivotable between an open position, in which the disc is substantially parallel to an axis through the housing, and a closed position in which the disc is generally transverse to the housing. The pivot axis of the disc is offset with respect to the main axis through the housing. The seal ring is installed on the disc and seals against the housing.
The commonly owned U.S. Pat. No. 4,281,817 discloses a similar valve in which the seal ring is in the housing and includes a radially inwardly projecting sealing surface which engages and cooperates with a peripheral seating surface of the disc to form a fluid-tight seal when the disc is in its closed position. In such valves provisions must be made for appropriately installing the seal ring in the housing. Typically, this involves the formation of an annular, enlarged diameter recess in a portion of the flow passage through the housing extending from an end thereof to an axially oriented face. The seal ring is placed against the face so that its sealing surface faces radially inward and a retainer ring, also disposed in the enlarged diameter conduit portion, is secured to the housing with threaded bolts which extend into the housing radially outward of the seal ring. The bolts pressure the retainer ring against the seal ring and the latter against the axially oriented face to securely install the seal ring in the housing and bias it into intimate contact with the axially oriented face to establish a seal between them. Thus, when the disc is closed and fluid pressure is applied to one side, fluid does not leak past the housing face-seal ring interface.
Seal ring installations as described in the preceding paragraph work well so long as the seal ring is constructed of a compressible material such as elastomers, for under relatively low pressure, low heat and/or with noncorrosive fluids or asbestos for installations subjected to higher temperatures and/or many types of corrosive fluids where conventional elastomers are not usable. Because of health hazards, however, the use of asbestos-based materials is no longer acceptable. In its stead it is now typically specified to employ metallic seal rings capable of withstanding the encountered temperatures, resisting corrosion by the fluid flowing through the valve and capable of establishing a seal with the closure member of the valve, e.g. the disc.
Although metallic seal rings are entirely satisfactory, from an operational point of the valve, it is much more difficult to prevent leakage past the interface between the valve housing and the seal ring as compared to seal rings constructed of relatively compressible materials. Metal seal ring installations require a significantly larger force with which the seal ring must be pressed against the cooperating, axially oriented face of the housing, and a relatively larger contact area between the two as compared to seal rings made of compressible materials such as asbestos, for example.
According to the prior art this force is generated by providing a retainer ring of the appropriate size so that it is strong enough to transmit the sealing pressure to the seal ring. Threaded bolts secure the retainer ring to the housing and generate the needed pressure. It is necessary that these bolts be placed radially outward of the outermost diameter of the seal ring. Since metal seal rings require a greater contact area with the opposing housing face to establish a seal and to prevent damage to the seal ring during operation, the bolts must be moved even further radially outward than was necessary for asbestos seal rings, for example. The extent to which the bolts can be moved radially outward, however, is limited by the standardized flanges at each end of the housing for connecting the valve with the pipeline in which it is installed. Moreover, the needed threaded holes in the housing have a tendency to weaken it which, for high pressure installations, might be unacceptable or outright dangerous.
There is, therefore, a present need for a metal seal ring installation for valve housings which are capable of generating the required, relatively large axial forces to engage the seal ring and seal it with respect to the housing so that leakage cannot occur when the disc is closed, while limiting the radial extent of the installation so as to not interfere with the connection of the valve to the pipeline and/or unacceptably weaken the housing.